On February 3rd Iranian TV broadcast a sneak peak at of their new Fateh class mini-subs. These appear to be the largest subs built by Iran so far and are still in development. The Fatehs are 500 ton boats that are 40 meters (130 feet) long. Boats this size are considered coastal subs. By way of comparison the most frequently used German sub during World War II (the 703 Type VIIs) were 769 tons and 67 meters (220 feet) long. The Type VII had a crew if 48, five torpedo tubes and 14 torpedoes. There was also an 88mm deck gun. The Type VIIs operated out in the mid-Atlantic and as far west as the East Coast of the United States and the Caribbean. The Fateh is meant to be a coastal sub and another German sub gives you a better idea of what the Fateh might be. A post-World War II German coastal sub, the Type 205, was similar in size to the Fateh. The Type 205s were designed in the early 1960s and were 450 ton, 44 meter (144 foot) long boats armed with eight torpedo tubes each loaded with a torpedo. There were no reloads. The 22 man crew had sufficient food and fuel on the boat to stay out for about four weeks. Unable to legally import military gear, Iran has adapted by manufacturing what it can, and that usually means older tech. So the Fateh will probably resemble the Type 205s in many ways.
The Fatehs are meant to be an extension of a growing family of Iranian mini-subs. In 2012 Iran completed its last (of 21) Ghadir class subs. The 120 ton Ghadirs were to have been succeeded by the 400 ton Nahang class. Alas, one Nahang entered service in 2006 and none followed. The Nahang seemed to spend most of its time in port, full of technicians, or in dry dock, partially disassembled. A successor to the Nahang, the 1,200 ton Qaaem has yet to be finished after seven years of effort. Moreover, the Qaaem, unlike the other Iranian built subs is not a mini-sub that can operate anywhere in the generally shallow Persian Gulf. For example, the three Russian built Kilo class subs Iran has are so big (2,300 tons) that they can only operate in about a third of the Persian Gulf. That makes them easier to find and destroy in the Gulf. That explains why Iran is increasingly sending its Kilos outside the Gulf and building more small boats.
The Faher appears to be the successor to the Ghadirs and apparently learned much from the failed Nahang class. The Ghadir is another example of Iranian resourcefulness in the face of embargoes. Since 1996, when Russia agreed to stop selling them submarines, Iran has been working on their own designs. After ten years of trial and error they produced the 120 ton Ghadir (Qadir) class vessels in 2005. The Iranians are not releasing specification sheets to anyone, but Ghadirs look very similar to the Italian Cosmos SX-506B submarines that Colombia has operated since the 1980s. The 100-ton SX-506Bs are only large enough to carry commandos and mines. However, released news footage shows what looks like to be two torpedo tubes on the Iranian Ghadirs. The Iranians claim that the Ghadirs carry torpedoes and have a crew of 18.
It should be remembered that Cosmos exported a number of larger vessels to Pakistan in the 1990s. Dubbed the SX-756 they may have been the design basis for the Ghadir. It should also be acknowledged that the North Korean Sang-O class submarine closely approximates the Ghadir type. In 2007, North Korea gave Iran, outright, four of its Yugo-type midget submarines. These Yugos were well worn 90-ton 21 meter (65 foot) craft but Iran accepted them all the same. Taking them apart taught the Iranians much about how to design and build mini-subs.
Iran took the big leap in the early 1990s, when they acquired three Kilo 877/636 type diesel electric submarines from Russia. The 2,300 ton Kilos are long range subs capable of operating throughout the Indian Ocean (from South Africa to Australia). The Kilos have six 533mm (21 inch) torpedo tubes and 18 torpedoes (including one or more Shkval rocket torpedo) or 24 mines. Very similar to the world-standard diesel submarine, the 1800-ton German Type 209, the Kilo is a formidable foe and can stay at sea for up to 45 days, which makes it capable of long range patrols.
All this Iranian submarine activity has spurred the U.S. to develop new tools and techniques for detecting small subs in shallow waters. The Americans have not released results of tests against NATO mini-subs. But that is to be expected. You save that kind of surprise for the first few days of a war.
Most of the submarines in service are diesel-electric and there are 39 nations operating a total of 400 diesel electric subs. Only three of these nations (China, Iran, North Korea) are likely to use their subs against the U.S. or its allies. China has fifty of these boats, Iran has three (plus 25 much smaller mini-subs) and North Korea has 20 (plus 50 much smaller mini-subs). So the U.S. has to worry about 150 diesel electric subs, half of them mini-subs. But about half of all these boats are elderly, obsolete, and noisy. That leaves about 70 subs that are a clear threat (though the older stuff can be a threat if you get sloppy). That’s a lot of subs, and they make the East Asian coast and the Persian Gulf dangerous places for American warships.